Chatham Islands skink

The Chatham Islands skink is a unique reptile endemic to the Chatham Islands of New Zealand. Despite being the only reptile in the region, it does not inhabit the main Chatham Island but is distributed across the other major islands. There is a hypothesis that a subspecies, Oligosoma nigriplantare nigriplantare, may have once existed on Chatham Island itself, but there is no fossil evidence or historical record to substantiate this.

On Pitt Island, the skink faces the threat of local extinction due to introduced mammals, which could pose a risk to its survival on Chatham Island as well. These skinks inhabit a variety of environments, including grasslands, shrublands, and rocky coastal areas with sparse vegetation.

Notably, the Chatham Islands skink exhibits significant variation in body size, coloration, and patterns. This diversity may be attributed to evolutionary changes since their colonization of the islands. Genetic research indicates that these skinks diverged from their closest relative, Oligosoma nigriplantare polychroma, approximately 5.86 to 7.29 million years ago, likely due to a single overwater dispersal event to the Chatham Islands.

Within the Chatham Islands, the skinks display noticeable phenotypic differences but minimal genetic divergence. This suggests that while there is limited gene flow between the islands, it has not resulted in the formation of new species. The genetic and morphological differences between the Chatham Islands skink and Oligosoma nigriplantare polychroma may even warrant classifying them as distinct species.